The actin-bundling protein cortexillin is the downstream target of a Rac1-signaling pathway required for cytokinesis.

During the process of cytokinesis by which eukaryotic cells constrict and divide in two, multiple cellular activities have to be precisely coordinated in space and time to guarantee equal distribution of chromosomes and cytoplasm to the emerging daughter cells. Eventually, constriction of the cleavage furrow leads to the complete separation of the daughter cells. Since the basic observation of cell division some 100 years ago, the principal challenge has been to unravel the detailed molecular mechanisms and signaling events leading to cytokinesis. Regulation of this fundamental cellular process is still poorly understood yet a central issue in modern cell biology. In the recent past it became evident that small GTPases of the Ras super family play a major role during this process. This review is focused on a Rho family GTPase-mediated signaling pathway that is required for cleavage furrow assembly and cytokinesis by the actin-bundling protein cortexillin of D. discoideum cells.